1. Field of the Invention
The present invention relates to forming features in a metal-containing web using a continuous etch process, and more particularly to forming accurately dimensioned features in a metal-containing web by a continuous etch process.
2. Description of the Related Art
Functional patterns formed into aluminum foil are used in a variety of products, including thin foil products such as microwave plates, trays and bowls, as well as thick foil products such as planar speakers, electronic circuitry surveillance products used for shoplifting prevention in retail environments, and flexible heaters, just to name a few. Common processes to form these products includes chemical milling or chemical etching of a metal-containing layer of a web. The metal-containing layer typically is a metal foil of aluminum or copper or, less commonly, silver having a desired thickness that is laminated to or otherwise formed on a suitable substrate. A desired pattern is formed on the surface of the metal foil with a etch resistant protective coating, typically by using Gravuere printing. The web with the printed metal foil is introduced to an etching solution, whereupon the metal foil in the open areas of the pattern is etched away to leave behind the desired protected features of the pattern. The etching bath can be acidic or basic in nature, depending on the type of metal. The foil can be of different thickness, depending on the intended function of the desired product. Typical foil thickness is from about 1 micron to about 15 microns and greater for microwave applications, from about 5 microns to about 50 microns and greater for planar speakers and flexible heaters, and from about 5 microns to about 70 microns and greater for electronic article surveillance products.
Continuous etching or milling processes are particularly advantageous when large amounts of patterned web is required because of the low cost per product unit relative to non-continuous processes. A particularly useful continuous demetallizing process-and apparatus are described in U.S. Pat. No. 5,340,436, which issued Aug. 23, 1994 to D. Gregory Beckett. Generally speaking, the apparatus has an elongate tank that holds a bath of aqueous etchant material. The web containing the metal layer to be etched initially is arranged in a roll. The web is taken off of the roll and guided into the bath at one end, guided either horizontally or sinusoidally through the bath, and removed from the bath and taken up on another roll at the opposing end of the bath. The web is driven along its path by any suitable drive mechanism. An example of a drive mechanism is a combination of driven belts and roller elements. The web passes between these elements, which engage the web and drive it.
The continuous etch process of the ""436 patent has commonly and successfully been used to make blanks for microwave plates, trays and bowls, but it also is useful in the large scale fabrication of items such as planar speakers, electronic circuitry surveillance products, and flexible heater elements, all of which are made from webs having thicker metal layers. Planar speakers have been known for many years but have not achieved widespread commercial success because of the relatively cost of manufacture of the diaphragm element. A schematic of an illustrative planar speaker diaphragm 100 is shown in FIG. 1, greatly simplified for purposes of clarity. FIG. 1 shows a thin conductive path 120 mounted on a thin insulating flexible substrate 110. A alternating audio current is established in the path 120 by an audio source 130. The dashed arrows indicate current flow at a moment in time. The current flow is shown in a counterclockwise direction, which establishes a magnetic field about the path 120 as indicated by the ovals with north indicated by xe2x80x9cNxe2x80x9d and south indicated by xe2x80x9cS.xe2x80x9d A force is induced on the diaphragm 100 due to the interaction of the magnetic field with a series of permanent magnets mounted behind the diaphragm 100 (not shown), causing the diaphragm to move in a direction indicated by the arrows marked xe2x80x9cM.xe2x80x9d The acceleration of the diaphragm 100 is a function of many variables, including the length, thickness and width of each trace in the conductive path as well as the number and spacing of the traces. The best conductive path includes a number of very thick but narrow traces of very specific design that are densely packed. The diaphragm 100 typically is the most expensive component of the planar speaker to make.
Accordingly, it is desired to make various products that include thick metal features, such as conductive traces used in speaker diaphragms, electronic circuitry surveillance products, and flexible heaters, at lower cost but without sacrificing the quality of the traces in the conductive path.
While continuous etch processes such as the process of the ""436 patent are useful in the fabrication of patterned product units on webs, they are not entirely satisfactory for etching product units that include thick conductive traces because the trace designs are distorted by the movement of the web through the bath. This and other disadvantages in using continuous etch processes in the fabrication of patterned webs that include thick conductive traces are overcome in the present invention, which in one embodiment is a metal-containing web for use in a continuous etch process to produce a product unit having at least one feature corresponding to an original feature design. The metal-containing web comprises a metal-containing layer and an etch-resistant layer disposed over the metal-containing layer. The etch-resistant layer has a pattern defining the feature, the pattern having portions transverse to a direction of elongation of the web being enlarged relative to corresponding portions of the original feature design.
Another embodiment of the present invention is a metal-containing web for use in a continuous etch process to produce a planar speaker product unit having at least one trace corresponding to an original trace design. The web comprises a substrate layer, a metal-containing layer disposed over the substrate layer, and an etch-resistant layer disposed over the metal-containing layer. The etch-resistant layer has a pattern defining the trace. The pattern has portions transverse to a direction of elongation of the web being widened relative to corresponding portions of the original feature design. The pattern also has portions parallel to a direction of elongation of the web being unmodified relative to corresponding portions of the original feature design.
A further embodiment of the present invention is a pattern-containing printing cylinder for printing a resist pattern on a web in a continuous etch process to produce a product unit having at least one feature corresponding to an original feature design. The pattern on the cylinder has portions transverse to a direction of rotation of the cylinder that are enlarged relative to corresponding portions of the original feature design.
Yet another embodiment of the present invention is a method of preparing a modified trace design having at least one trace for use in effecting selective demetallization of a metal-containing web in a continuous etch process. The method comprises conceiving an original trace design; envisioning placement of the original trace design on the web, wherein at least some segments of the original trace design are transverse to a direction of elongation of the web; and widening at least some of the segments of the original trace design that are transverse to a direction of elongation of the web to obtain the modified trace design.
A further embodiment of the present invention is a method of preparing a practical feature design for use in effecting selective demetallization of a metal-containing web in a continuous etch process. The method comprises conceiving an ideal feature design; envisioning placement of the ideal feature design on the web, wherein at least some portions of the ideal feature design are transverse to a direction of elongation of the web; and widening at least some of the portions of the ideal feature design that are transverse to a direction of elongation of the web to obtain the practical feature design.
Yet another embodiment of the present invention is a method of effecting selective demetallization of a web in accordance with a feature design, the web being formed by a layer of aluminum supported on flexible substrate layer. The method comprises applying a sodium hydroxide-resistant material to the aluminum layer, the sodium hydroxide-resistant layer comprising a pattern for defining the feature and the pattern having portions transverse to a direction of elongation of the web, a substantial number of the transverse portions of the pattern being enlarged relative to corresponding portions of the feature design; continuously passing the aluminum layer in an immersed condition through a bath of aqueous sodium hydroxide based solution to effect removal of aluminum from areas of the web not protected by the pattern; and washing the aluminum layer free from spent sodium hydroxide based solution.